from math import factorial

N = int(input())

ans = 0

if N % 2 == 0:
    for i in range(N+1):
        if i%2 == 0:
            m = (N-i)//2
            ans += factorial(i+m)//(factorial(i)*factorial(m))
else:
    for i in range(N+1):
        if i%2 == 1:
            m = (N-i)//2
            ans += factorial(i+m)//(factorial(i)*factorial(m))

print(ans)